1. Field of the Invention
The present invention relates generally to a system and method for controlling coasting of a hybrid vehicle equipped with an Automated Manual Transmission (AMT), and, more particularly, to a technology for controlling the amount of regenerative braking when a vehicle is coasting.
2. Description of the Related Art
The power system of a hybrid vehicle equipped with an AMT according to the present invention is made up of an engine, a clutch, a motor, and an AMT, and is configured such that the speed transmission of the AMT is realized when a clutch is released, and that both the power of the engine and the power of the motor are supplied to the input shaft of the AMT when the clutch is engaged.
Hybrid vehicles generally improve energy efficiency by collecting the drive inertia of the vehicle using a regenerative braking function. This regenerative braking function is required to be properly harmonized with the coasting properties of a vehicle. That is, it is necessary to increase the distance of coasting by reducing the amount of regenerative braking when a driver wishes to allow the vehicle to coast and it is necessary to increase the amount of energy recovery by increasing the amount of regenerative braking when coasting is not greatly necessary.
In order to adjust the above-described coasting properties and the regenerative braking function, certain systems and methods of interlocking the degree of manipulation of a brake pedal, operated by a driver, with the amount of regenerative braking have been developed. However, these techniques can be used only in a system capable of obtaining information about the degree of manipulation of a brake pedal. In a system which can only confirm whether a brake pedal is operated or not, it is difficult to adjust the coasting properties and the regenerative braking function based on the degree of manipulation of a brake pedal.
Furthermore, it is difficult to obtain the above-described information about the degree of manipulation of a brake pedal in large-sized commercial vehicles, so that such a vehicle uses a conventional method shown in FIG. 1 to realize the regenerative braking function. That is, when a driver's foot is taken off an accelerator pedal and the value of an accelerator pedal sensor is not greater than 0, a deceleration request torque, which has been predetermined based on a vehicle speed, is obtained at step S510, and then regenerative braking corresponding to the deceleration request torque is performed.
For reference, when the deceleration request torque is not greater than the maximum regenerative torque of a motor, that is, the maximum regenerative braking torque which can be realized by a motor, regenerative braking is performed using only a motor while releasing a clutch at step S520. Otherwise, the clutch is engaged, so that the regenerative braking force of a motor is added to the friction of an engine, thereby performing control such that the deceleration request torque is satisfied at step S530.
Meanwhile, with regard to the portions of FIG. 1 which have not been described, when the value of the accelerator pedal sensor is greater than 0, the maximum drive request torque, which has been previously mapped to the input-shaft rotational speed of transmission, is multiplied by the degree of the operation of the accelerator pedal sensor at step S540, thereby obtaining a drive torque to be output to the drive shaft of a vehicle. Further, the drive torque is generated using both the engine and the motor at step S550, thereby accelerating the vehicle.
Here, a situation where regenerative braking corresponding to a deceleration request torque is performed using a motor will be described. It can be seen that, when a driver takes his/her foot off an accelerator pedal, regenerative braking corresponding to a deceleration request torque, which has been preset, takes place according to a vehicle speed at that moment. In this case, even when the driver wants to increase the coasting distance of a vehicle by decreasing the amount of deceleration of the vehicle, this intention of the driver cannot be realized.
Therefore, if a vehicle speed decreases and the coasting distance is short due to an undesired level of regenerative braking when a driver takes his/her foot off an accelerator pedal, the driver typically steps on the accelerator pedal again in order to gain speed, thereby accompanying the frequent connection and disconnection of the clutch. Therefore, driving quality decreases because of the impact caused by the connection/disconnection, fuel efficiency is negatively affected, and the durability of the clutch decreases.
The contents, described as related art, are only intended to provide an understanding of the background of the present invention, and should not be understood that the present invention corresponds to already-known related art by those skilled in the art.